Catalytic alkylation processes are commonly used for the production of monoalkylaromatics from olefins and aromatics. One commercialized application of this process is for the conversion of ethylene and benzene to ethylbenzene that may subsequently be used, for example, to produce styrene.
The catalytic alkylation of benzene with ethylene to produce ethylbenzene is very exothermic and the associated ethylbenzene production systems need to manage the heat generated to control the product outlet temperatures of the reactors. If a reactor is built for higher outlet temperatures, its construction cost will be higher because more expensive materials are required to handle the higher temperatures. To control the outlet temperatures, many ethylbenzene production processes use reactors that have thermally-insulated catalytic sections with cooling provided between these sections to remove excess heat. Additionally, relatively high benzene to ethylene (BE) molar ratios for feeding benzene and ethylene, e.g., BE ratios of about 5 or 6, to the reactors are used. Because the feed is benzene-ultra-rich, high amounts of unreacted or excess benzene are available throughout the reactor to act as a heat sink to further control the rise in process temperatures. As a consequence of the excess benzene, the cost of many ethylbenzene production systems and the expense of their operation are high because larger reactors and more elaborate and expensive recycling sub-systems are required to handle the additional volume of benzene.
Recently, some of the ethylbenzene production apparatuses are being built to operate at lower inlet temperatures for operation at lower BE ratios for the introduction of benzene and ethylene into the catalytic sections of the reactors. Unfortunately, the various catalysts currently available for alkylation of benzene with ethylene either have relatively low activity or they deactivate rapidly at lower temperatures and need to be replaced more often. Because the cost of replacing a catalyst is very expensive, a less active and more stable catalyst is often used to reduce the frequency of catalyst replacement. Using a less active catalyst means that more catalyst must be used, thereby increasing cost, to achieve an equivalent yield of ethylbenzene that would otherwise be achieved using a more active catalyst.
Accordingly, it is desirable to provide methods and apparatuses for producing ethylbenzene using relatively low inlet temperatures and low BE ratios without the high cost associated with frequent catalyst replacement. Moreover, it is desirable to provide methods and apparatuses for producing relatively high yields of ethylbenzene using relatively low inlet temperatures and low BE ratios without the cost associated with using additional catalyst. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent Detailed Description of the Invention and the appended Claims, when taken in conjunction with the accompanying drawings and this Background of the Invention.